Processing of biological samples on glass slides has a long history. Compared to the relatively simple dyes and stains of previous years, many newer techniques for analysis are significantly more complex and the reagents considerably more expensive. Immunoassays, hybridization assays, and in situ nucleic acid amplification assays are particularly demanding in terms of reagent expense, need for accurate timing, and need for precise temperature control. These are particularly demanding because the reagents should be applied in a precisely controlled thickness. Further, some of these assays involve heating of the slide and reagents to produce enzymatic reactions, yet the reagents must not evaporate during the procedure. In addition, it is desirable to have the assays performed automatically to whatever extent is possible, both to save cost and for increased reliability and precision.